Kod


     <!DOCTYPE html>
<html lang="pl">
<head>
    <meta charset="UTF-8">
    <style>
        *{
            padding: 10px;
            text-align: center;
        }
        #calosc {
            width: 80%;
            margin-left: auto;
            margin-right: auto;
        }
        #logo{
            background-color: blue;
            min-height: 100px;
            color: white;
        }
        #lewa{
            background-color: rgb(100, 100, 200);
            min-height: 100px;
            width: calc(33.3333% - 20px);
            float: left;
        }
        #srodek{
            background-color: #a6edb9;
            min-height: 100px;
            width: calc(33.3333% - 20px);
            float: left;
        }
        #prawa{
            background-color: pink;
            min-height: 100px;
            width: calc(33.3333% - 20px);
            float: left;
        }
        #dol{
            background-color: lightblue;
            min-height: 100px;
            clear: both;
        }
    </style>
</head>
<body>
    <div id="calosc">
        <div id="logo">
            <h1>Moja strona</h1>
        </div>
        <div id="lewa">
            <?php
                $a=rand(1,100);
                echo $a;
            ?>
        </div>
        <div id="srodek">
            <?php
                $b=rand(1,100);
                echo $b;
            ?>
        </div>
        <div id="prawa">
            <?php
                $c=rand(1,100);
                echo $c;
            ?>
        </div>
        <div id="dol" style="background-color: red;">
            <?php
                $suma = $a+$b+$c;
                echo "sqrt($a+$b+$c)=".sqrt($suma)."<br>";
                echo "$a+$b+$c=$suma";
            ?>
        </div>
    </div>
</body>
</html>